Wow. You reinforce how thankful I am to have such a spectacular bf. I was listening to Howard Stern and a famous chick (name escapes me) was talking about 3somes. She's says they are fine if you don't mind ruining the relationship. She says it's because once the guy gets a taste of a 3some something inside them changes. Like the bar has eternally been lifted and sex with just their partner is no longer exciting.
Some couples can do it. We had friends that had an open relationship with 3somes and such for 12 years.
We are a pretty strong couple and we could probably do it, but chancing it isn't worth it.
